Scripture often speaks of our union with Christ. It does this wherever it tells us that we are “in Christ.” The word “in” speaks of a union. If the branch is in the vine, then the vine and branch are united. So also, to be in Christ means to be united to him. And so the Corinthians were “them that are sanctified in Christ Jesus” (1 Cor. 1:2). The Ephesians were the “faithful in Christ Jesus” (Eph. 1:1). The Philippians were “the saints in Christ Jesus” (Phil. 1:1). The Colossians were the “saints and faithful brethren in Christ” (Col. 1:2). The Thessalonians were the church “which is in God the Father and in the Lord Jesus Christ” (1 Thess. 1:1). All of these churches were in Christ. That is the language of union. So also you and I who believe are in Christ. Our “life is hid with Christ in God” (Col. 3:3). You and I live, “yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me” (Gal. 2:20).

Union with Christ.

From one point of view, this is a very simple truth to understand: I am united to Jesus Christ.

From another point of view, this is a very difficult truth to grasp. I am united to Jesus Christ, but Jesus is in heaven, and I am on earth. We are in different places. How can I be united to him? What is more, I cannot see our union with my eyes, I cannot hear it with my ears, I cannot lay my hand upon it. If I cannot sense this union with my physical senses, then what exactly is this union with Christ?

Because of the impossibility of sensing this union with our physical senses, John Calvin and other Reformed theologians have called our union with Christ the mystical union. By this description, they meant that our union with Christ is a real union, but it is not a physical union. The word “mystical” means something that is not physical, something that cannot be sensed with our physical senses, but which is nevertheless real and spiritual and deep. Even though Jesus, according to his human nature, is in heaven, he is still present with us by this mystical union. And even though we are on earth, we are still united to Jesus through this mystical union.
Union with Christ.

The mystical union.

But what is it? What is this union? That is the hard question we must answer.

So let’s start simple. What is union with Christ? This: Union with Christ is the real, spiritual connection between Jesus Christ and his people. It is the real, spiritual connection between Jesus Christ and me. Although Jesus is in heaven, and I am on earth, we are truly, really, spiritually connected to each other. We are in separate places, but we are not separate from each other. We are united! We are connected. And notice that the connection is spiritual. That is why we cannot see it with our eyes, hear it with our ears, or otherwise detect it with our physical senses. It is spiritual. But it is a very real connection for all that. It is a connection that we can detect spiritually and that we enjoy spiritually.

This spiritual connection is union with Christ.

This spiritual connection is the mystical union.

We can go further. We can describe the character of the connection between Christ and us. Let’s begin with Christ. Union with Christ means that Christ dwells with us. Although Christ according to his human nature is in heaven, he is always present with us according to his divine nature. He is truly man, but he is also truly God. And as God, he dwells with us. As the Heidelberg Catechism says, “with respect to His Godhead, majesty, grace, and spirit, He is at no time absent from us” (Lord’s Day 18, Q&A 47). Further, he dwells in us. There is that word “in” again: a word that speaks of union. Jesus said about his people, who love and obey him in gratitude for salvation, “If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him” (John 14:23). A little later, Jesus said about us, “I in them…” (John 17:23). The connection between Christ and us is that he indwells us.

Let’s also look at it from the other point of view. What does it mean that we are connected to Christ? It means that we are incorporated into him. The word “incorporated” simply means that we are members of his body. We form one spiritual organism, with our Lord as the head, and with us as so many members of his body. As Paul wrote, “For as the body is one, and hath many members, and all the members of that one body, being many, are one body: so also is Christ…Now ye are the body of Christ, and members in particular” (1 Cor. 12:12, 27).

Union with Christ.

The mystical union.

Christ indwelling us, and we incorporated into him.

We can go even further yet. We can precisely identify what the connection is between Christ and us. First, the union between Christ and us is the Holy Spirit. Our Savior has given us his own Spirit, who now dwells in both Christ and us, uniting us as one. As the Heidelberg Catechism says, we “become more and more united to [Jesus’] sacred body by the Holy Ghost, who dwells both in Christ and in us; so that we, though Christ is in heaven and we on earth, are notwithstanding flesh of his flesh, and bone of his bone; and that we live and are governed forever by one Spirit, as members of the same body are by one soul” (Lord’s Day 28, Q&A 76).

Second, the union between us and Christ is faith, which the Holy Spirit works in our hearts. Faith is an ingrafting into Christ (Rom. 11:17, 20; Lord’s Day 7, Q&A 20). Faith is abiding in the vine (John 15:1–8). Faith is embracing Jesus Christ (Belgic Confession, Article 22). All of these descriptions show that faith is that real, spiritual connection between God’s people and Christ.

Union with Christ.

The mystical union.

The Holy Spirit, who works faith in our hearts.

The truth of union with Christ is encouraging to God’s people. It is encouraging to the young person. This truth teaches you that you have Christ. You have Christ! You have him dwelling in you, and you are incorporated into him. He is the Savior who brings the good news of salvation from sin and death (Luke 2:10, 11). And he is yours! He is the Lamb of God, which taketh away your sins by his precious blood (John 1:29). And he is yours! He is the Advocate, who makes intercession with God for you (1 John 2:1). And he is yours! He is the Friend that sticketh closer than a brother (Prov. 18:24) when you are lonely. And he is yours! He is the great Physician (Luke 5:31, 32), who heals our deadly disease by taking away our sin. And he is yours! You are united to him.

Therefore, the truth of union with Christ is also a help to God’s people in living their Christian lives. It is a help to the young person. When the devil tempts you in your car to listen to the world singing about its pride and its lust and its warped idea of what makes life good, then you remember, “I am united to Christ! He dwells in me, and I will not make Christ listen to such things!” When strange women tempt you online to view their shameful deeds, then you remember, “I am united to Christ, and I will not make Christ view such things!” When an evil spirit of hatred tempts you to laugh at the godly classmate who is different, then you remember, “I am united to Christ, and I will not let Christ hear me laugh at one of his own.”

Union with Christ.

The mystical union.

All glory be to God!